Currently, there is great interest in the desulfurization and denitrogenation of gasoil destined for the production of diesel for the natural compounds of sulfur and nitrogen present in gasoil are transformed by means of combustion into SOx and NOx, which are the main sources of acid rain and air pollution. In order to face the challenge of producing fuels with low sulfur and nitrogen contents, the refining industry uses hydrodesulfurization catalytic processes (HDS) and simultaneously hydrodenitrogenation (HDN), which use harsh conditions and consume high hydrogen amounts.
It is well known that the nitrogen organic compounds (NOCs) present in the Straight Run Gasoil (SRGO), Light Cycle OIL (LCO) and Coker Gasoil (CGO) loads exert an inhibiting effect on the catalytic activity of HDS reactions, especially from heteromolecules with high steric impediments and high HDS refractory characters like alkyl-dibenzothiophenes such as 4,6-DMDBT. The NOC's compete with the sulfur organic compounds for the active sites of the catalysts used in the HDS process, poisoning them, which leads, on the one hand, to use huge catalyst volumes, and on the other hand, to establish highly severe reaction conditions in order to keep the conversion and selectivity levels, which reduces significantly the lifespan of the catalysts, affecting considerably the economy of the production process of ultra-low-sulfur diesel (ULSD below 15 ppm).
The production of fuels, according to the European Union Environmental Norms established for 2005, requires the reduction of the sulfur amount in diesel and gasoline at levels that are equal or below 10 parts per million weight (ppmw). For example, in Germany, the reduction of the sulfur amount in gasoline and diesel up to 10 ppmw was proposed in 2005 whereas in the United States of America the norm for the maximum sulfur content in diesel is limited to 15 ppmw from 2006.
In the case of Mexico, PEMEX Refining, honoring its commitment to produce and distribute diesel and gasoline that follow the environmental legislations under international quality standards, is adjusting its gasoline and diesel production parameters under the Mexican norm NOM-086-Semamat-Sener-SCFI-2005, which sets a maximum sulfur content in diesel of 15 ppmw.
Therefore, for the production of ultra-low-sulfur diesel, it is necessary that the HDS process have an efficiency rate above 99.9% in the reduction of sulfur organic compounds present in the hydrocarbon blend, where benzothiophenes and alkyl-dibenzothiophenes are found.
Various studies have shown that the HDS catalytic reaction is significantly inhibited by the NOCs. A competitive adsorption process among the nitrogen and sulfur compounds for the catalyst active sites occur, which provokes that the nitrogen compounds poison the HDS catalysts. The inhibition extent depends on the type and concentration of NOC's. In HDS feedstocks consisting of SRGO, the average content of total organic nitrogen is from 100 to 300 ppm whereas in heavier currents such as LCO, the total nitrogen content is above 500 ppm (Georgina C. Laredo et al., Nitrogen compounds characterization in atmospheric gas oil and light cycle oil from a blend of Mexican crudes. Fuel 81 (2002) 1341-1350).
Some researchers have studied the poisoning effect on HDS catalysts by NOC's, finding that even 3-ethylcarbazole traces could have an enormous effect on the HDS of 4,6-diethyldibenzothiophene because the alkyl carbazoles, in spite of being very difficult to react with, the could be adsorbed and block the active sites of the HDS catalyst.
Due to the aforementioned, an attractive technological alternative that has been proposed to solve these problems is the use of a pretreatment process for the reduction of NOC's from the HDS currents; the alternative consists of the use of physical adsorption methods at ambient temperature for the selective removal of NOC's. In order to an adsorption process to be a viable technological alternative, various characteristics are required to be met, where the following are the most important: ambient temperature, atmospheric pressure, no hydrogen use, use of adsorbents with high Intrinsic adsorption capacity, highly selective towards NOC's and easily regenerated.
Among some of the technologies that have been developed for the removal of NOC's by means of the adsorption process, the process reported in the U.S. Pat. No. 6,248,230 B1, Jun. 19, 2001, Min et al., Method for manufacturing cleaner fuels is found. In this process, the use of solid adsorbents that include activated alumina, acid white clay, Fuller's earth, activated carbon, zeolite (type not specified), cation exchange resins, hydrated alumina and silica gel is reported. During the research process to select the materials, it was found that the most suitable one was silica gel with a pore diameter from 40 to 200 Å, specific surface from 100 to 1,000 m2/g and pore volume from 0.5 to 1.5 cc/g.
This enterprise developed a demonstration plant to treat 1,000 B/D, using a combination of adsorbent materials such as silica gel and ionic exchange resins. As for the regeneration process of the adsorbents, the patent reports on the use of a non polar solvent (n-hexane) for the first step, and afterwards, the use of a highly polar solvent which is methyl tert-butyl ether (MTBE).
In the patent request US 2010/0300935 A1, Dec. 2, 2010, Nicolaos et al., Process for desulfurization and denitration of a gas-oil-type hydrocarbon fraction that contains nitrogen compounds, a process for the desulfurization and denitrogenation of a fraction of gasoil-type hydrocarbons containing nitrogen compounds is described. The HDS process is preceded by an adsorption unit of nitrogen compounds that inhibit the HDS reactions. The adsorbents for which the process was designed were selected among the families of ionic exchange resins, activated carbons, silicas, aluminas, zeolites, metal oxides or reduced metals, being also possible the use of mixtures of solids belonging to any of the previously mentioned various families.
Preferably, an adsorbent belonging to the zeolite family is used, and more specifically, a solid adsorbent consisting of faujasite-type zeolites, X or Y, with an atomic Si/Al ratio above 1. As for the regeneration process, it is performed through the treatment of the exhausted adsorbent with a current of already-treated gasoil (with a very low nitrogen and sulfur concentration) in order to adsorb the nitrogen and sulfur compounds retained in the adsorbent; the treatment temperature is 180° C.
In the patent request US 2009/0107882 A1, Apr. 30, 2009, Zheng et al., Adsorbents for denitrogenation desulfurization of hydrocarbon oils and methods of producing, a series of adsorbents, their synthesis procedure and use to adsorb CONs and sulfur organic compounds present in vehicle fuels at ambient temperature and atmospheric pressure are described. The adsorbents are based on transition metal phosphides which can be or not supported on zeolites, titania or alumina; an example of these materials are the NiP/TiO2 and WP/TiO2—ZrO2 systems.
The present invention differs from patent documents U.S. Pat. No. 6,248,230 B1, US 2010/0300935 A1 and US 2009/0107882 A1, in both the type of employed adsorbent materials and the preparation of extrudates and the regeneration of the used adsorbent materials. In this sense, it is important to point out that the process of the present invention is a viable technological alternative to reduce the content of NOC's present in the diesel HDT loads at ambient temperature and atmospheric pressure without using hydrogen by means of adsorbent materials that showed high intrinsic adsorption capacity and selectivity towards NOC's, in addition to be easily regenerated.
Additional materials that have been reported for this purpose are silica gel, copper zeolites, acceptor materials, methyl viologen aluminosilicates (MV-AS), exhausted FCC catalysts, activated alumina (AA), activated carbon (AC) and mesoporous molecular sieves (MMSs).
Recently, it has been reported that the materials with metal organic frameworks (MOF: Metal Organic Framework) that develop surface areas from 3,000 to 10,000 m2/g, depending on their porous structure, have great possibilities to be applied in various fields such as catalysis, gas storage and separation processes.
The MOF MIL-101-Cr (MIL: Material of Institut Lavoisier) showed itself to be capable of removing nitrogen organic compounds from liquid hydrocarbon currents, SRGO, LCO and model blends, Alexey L. Nuzhidin et al., Removal of nitrogen compounds from liquid hydrocarbon streams by selective sorption on metal-organic framework MIL-101. Mendeleev Commun., 2010, 20, 57-58. This MOF has the property of developing a specific surface of up to 5,900±300 m2/g; in the adsorption tests, it was found that it is capable of adsorbing 9.0 mg of nitrogen/g of adsorbent from a SRGO that contained 131 mg of nitrogen/kg of SRGO.
Afterwards, a comparative study of the adsorption capacity of the series of mesoporous metal methylcarboxilates, MOFs with different topologies and compositions was carried out; MIL-100(Fe), MIL-100(Cr), MIL-100(Al), MIL-101(Cr), [Cu3(BTC)2], CPO-27Ni, CPO-27(Co) and MIL-47/MIL-53 with model blends from a series of nitrogen compounds: indole, 2-methylindole, 1,2-dimethylindole, carbazole, and N-Methylcarbazole dissolved in toluene/n-heptane blends, Michael Maes et al., Selective Removal of N-Heterocyclic Aromatic Contaminants from Fuels by Lewis Acidic Metal-Organic Frameworks. Angew. Chem. Int. Ed. 2011, 50, 4210-4214.
Such study reported that the MOFs MIL-100 and MIL-101 are the most promising to adsorb nitrogen compounds selectively, considering the presence of sulfur organic compounds whereas the [Cu3(BTC)2], CPO-27N, and CPO-27(Co) materials adsorb both nitrogen and sulfur compounds.
According to Imteaz Ahmed et al, Adsorptive denitrogenation of model fuels with porous metal-organic frameworks (MOFs): Effect of acidity and basicity of MOFs, Applied Catalysis B: Environmental, 129 (2013) 123-129, an acidic functionalized MOF AMSA MIL-100 (Cr) can help to the selective removal of certain slightly basic compounds such as sulfur compounds, mainly when they are present at low concentrations, due to basic acid interactions, however, it is not useful to increase the adsorption of neuter compounds such as indole.
The materials employed in the present invention are adsorbent materials with metal organic framework MIL-101-Cr-MX+, where MX+ can be any metal cation such as Mg2+, Al3+ or Ti4+, materials with high crystallinity and high surface area with the metal cation highly dispersed. This type of MOF has a zeolite-type structure, which consists of two-cavity-quasi-spherical cages (2.9 and 3.4 nm) accessible through 1.2- and 1.6-nm windows. These materials have high surfaces and pore volumes (in general from 3,200 to 3,900 m2/g and from 1.4 a 2.1 cc/g, respectively), they also have very good resistance to common solvents and thermal stability (Fe-MIL-101 up to 180° C. and Cr-MIL-101 up to 300° C.). The MIL-101 structure consists of terephthalate radicals that work as ligands of methyl M3O-carboxilate trimers (M=Fe or Cr). These metal ions display an octahedral coordination with water molecules at bond ends. It has been reported that the water molecules (two water molecules per trimeric group according to elemental and thermogravimetric analyses) can be easily eliminated by means of a thermal treatment under vacuum, thus providing coordinatively unsaturated, catalytically active sites (Young Kyu Hwang et al., Selective sulfoxidation of aryl sulfides by coordinatively unsaturated metal centers in chromium carboxylate MIL-101. Applied Catalysis A: General 358 (2009) 249-253).
Therefore, there is a great need for having adsorbent materials capable of removing NOC's selectively from SRGO, LCO, CGO currents and their blends at atmospheric pressure, ambient temperature without hydrogen consumption, in addition to be easily regenerated.
The use of this type of materials either as adsorbents or any other technological application becomes difficult because these materials, when synthesized, are obtained as powders. For a viable technological application such as their use in continuous processes of the fixed-bed-column type (FBC) or any other related process, in adsorption operations of gases such as hydrogen and CO2 or in selective adsorption processes of N and S heteromolecules in fixed bed, it is necessary to form extrudates.
These materials have been extrudated by means of eccentric presses and certain binders that can be: titanium dioxide and hydrated titanium dioxide (U.S. Pat. No. 5,430,000, Jul. 4, 1995. Timken, Method for preparing titania-bound zeolite catalysts), hydrated alumina and other aluminas (WO 94/29408, Dec. 22, 1994. Keville et al., Process for preparing an alumina bound zeolite catalyst), mixtures of alumina and silicon compounds (WO 94/13584, Jun. 23, 1994. Miller, Preparation of aluminosilicate zeolites), silicon compounds (EP 0 592 050 B1, Apr. 10, 1996. Klazinga et al., Process for extruding crystalline aluminosilicates), clays, alkoxysilanes (EP 0 102 544 81, Jun. 1, 1988. Hoelderich et al., Process for the production of hard fracture-resistant catalysts from zeolite powder), amphiphilic materials and graphite (U.S. Pat. No. 6,893,564 B2, May 17, 2005. Mueller et al., Shaped bodies containing metal-organic frameworks).
For this purpose, various patents have been presented: the U.S. Pat. No. 7,931,960 B2, Apr. 26, 2011, Hesse et at, Shaped bodies containing metal-organic frameworks shows a process where MOF tablets are prepared and molded from 1 to 16 mm in size, displaying good surface characteristics and mechanical resistance. These materials are prepared by means of an eccentric press Korsh (EKO type) from a MOF mixture (99.8%) with graphite (0.2%). The procedure is carried out under nitrogen atmosphere. In one of the examples, from a MOF-5 with BET area of 1,796 m2/g as powder, extrudates with 3-4.5 mm in diameter and 3 mm in length with BET areas of 1,532, 1,270 and 1,137 m2/g at applied pressures of 10, 28 and 51 N, respectively, were obtained.
Gregory W. Peterson et al. (Effects of pelletization pressure on the physical and chemical properties of the metal-organic frameworks Cu3(BTC)2 and UiO-66, Microporous and Mesoporous Materials, Volume 179, 15 Sep. 2013, Pages 48-53, http://dx.doi.org/10.1016/j.micromeso.2013.02.025), prepared extrudates following a method similar to the one reported in the U.S. Pat. No. 7,931,960 B2.
The technique state known by the applicant, represented mainly by the technologies described in the referred patent documents, is surpassed by the present invention, for such technique state refers in general terms to the use of MOFs in the reduction of nitrogen organic compounds (NOCs), but none specifically to the adsorbent materials with organic metal structure MIL-101-Cr-MX+ (MOF MIL-101-Cr-MX+), where MX+ can be any metal cation such as Mg2+, Al3+ or Ti4+, to reduce the NOC's present in hydrotreating (HDT) loads for the production of ultra-low-sulfur diesel (ULSD below 15 ppm).
The diesel HDT loads, to which the present invention is referred, are hydrocarbon currents with distillation temperatures ranging from 150 to 400° C., preferably Straight Run Gasoil (SRGO), Light Cycle OIL (LCO) and Coker Gasoil (CGO), including their blends, but oil derived fuels can be included: gasoline, diesel and jet fuel, and other hydrocarbon currents obtained from the oil refining processes, which in turn are destined to be loads of the hydrodesulfurization process (HDS) to produce ultra-low-sulfur diesel.
Thus, an item of the present invention is to provide a selective adsorption process to reduce the content of NOC's present in the diesel HDT loads, which takes place at ambient temperature, atmospheric pressure and without using hydrogen by means of adsorbent materials with organic metal structure MIL-101-Cr-MX+ (MOF MIL-101-Cr-MX+), where MX+ can be any metal cation such as Mg2+, Al3+ or Ti4+.
An additional item of the present invention is to provide a selective adsorption process to reduce the content of NOC's present in diesel HDT loads, which considers the preparation of extrudates for a viable technological application such as their use in continuous processes of the fixed-bed-column type (FBC) or any other related process.
Another additional item of the present invention is to provide a selective adsorption process to reduce the content of NOC's present in diesel HDT loads, which considers the regeneration of the used adsorbent MOF materials.
The aforementioned and other items of the present invention will be established more clearly and in detail in the following chapters.